<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
   /*     圣杯布局*/
        .HolyGrail {
            display: flex;
            min-height: 100vh;
            flex-direction: column;
        }
        header,
        footer {
            flex: 1;
            background:yellow;
        }
        .HolyGrail-body {
            display: flex;
            flex: 1;
        }
        .HolyGrail-content {
            flex: 1;
        }
        .HolyGrail-nav, .HolyGrail-ads {
            /* 两个边栏的宽度设为12em */
            flex: 0 0 12em;
        }
        .HolyGrail-nav {
            /* 导航放到最左边 */
            order: -1;
        }

        @media (max-width: 768px) {
            .HolyGrail-body {
                flex-direction: column;
                flex: 1;
            }
            .HolyGrail-nav,
            .HolyGrail-ads,
            .HolyGrail-content {
                flex: auto;
            }
        }
    </style>
</head>
<body class="HolyGrail">
<header>header</header>
<div class="HolyGrail-body">
    <main class="HolyGrail-content">HolyGrail-content</main>
    <nav class="HolyGrail-nav">HolyGrail-nav</nav>
    <aside class="HolyGrail-ads">HolyGrail-ads</aside>
</div>
<footer>footer</footer>
</body>
</html>